Longitudinal distribution and lateral pattern of megalopal settlement and juvenile recruitment of Carcinus maenas (L.) (Brachyura, Portunidae) in the Mira River Estuary, Portugal

Abstract

Settlement is a critical process in the life history of crabs, and thus affecting the abundance, distribution and structure of estuarine communities. The spatial pattern of settlement of megalopae of the shore crab Carcinus maenas along a longitudinal estuarine gradient (Mira River Estuary, Portugal) was examined, as well as its effects on the juvenile population. To measure megalopal settlement, four replicate collectors were deployed in six equally spaced stations along the estuarine axis. Juveniles were collected on the same locations with a quadrat randomly deployed on the substrate. To assess fine-scale megalopal settlement within a curved region of the estuary, replicate collectors were deployed on both margins along Moinho da Asneira curve. Megalopae settled differently along the six longitudinal points, with a tendency to attenuate their settlement upstream. Within the curved region, megalopae preferentially settled on the left margin collectors, probably due to the weaker velocity speeds felt on this margin. Concerning the overall juvenile density, there were significant differences among the stations distributed along the estuary, but they did no reflect a longitudinal dispersion attenuation pattern. Size-frequency distribution of the juvenile population showed that the average size is higher on the left margin. Recruits (carapace length between 1.0 mm and 3.4 mm) were more abundant on the upstream stations. Density of early juveniles (3.4 mme6.5 mm) and juveniles (6.5 mme10 mm) was more stable throughout the estuary axis than that of recruits. This distribution pattern may result from tidal excursion processes or mechanisms to avoid biotic interactions, such as predation and competition.

Cannibalism, post-settlement growth rate and size refuge in a recruitment-limited population of the shore crab Carcinus maenas

“…Because cannibalism is quite frequent in C. maenas and size-structured populations develop over that time, very marked density-dependent regulation is expected to be common. First crab instars and sub-adults may coexist in small nursery patches, leading to potential relative prey sizes smaller than 10% (Almeida et al, 2008;Silva et al, 2006), thus favouring cannibalistic interactions. The extent to which these different cohorts can coexist is therefore a crucial variable determining the persistence and stability of shore crab populations.…”

Simple model of megalopal transport in narrow river-dominated estuaries

“…Silva et al (2006) found that the settlement rates of Carcinus maenas L. (Brachyura, Portunidae) megalopae were highly variable along the longitudinal axis of an estuary in the Mira River Estuary in Portugal. The lower estuary, however, was less variable and had higher megalopa settlement rate.…”

Explaining Ocean Warming: Causes, scale, effects and consequences

“…For example, estuarine regions can provide refuge for cold-water species at lower latitudes. This has been well-demonstrated along the Iberian Peninsula for a variety of intertidal species, including fucoids (Lorenzen, 2007;Neiva et al, 2012), Carcinus maenas (Silva et al, 2006) and Patella vulgata (FischerPiette, 1955), although the underlying processes are not clear. Enclosed seas (e.g.…”